An ion beam irradiation system, which is a rotating irradiation therapy apparatus, treats cancer by irradiating an affected part of a patient's body with a proton beam, carbon ion beam, or other ion beam.
The ion beam irradiation system includes a rotating gantry, which is a rotating irradiation therapy apparatus. As disclosed, for instance, in Patent Document 1, the rotating gantry includes a front ring, a rear ring, and a gantry cylinder for connecting the front and rear rings. A beam transport device (beam path), which guides an ion beam, and an irradiation device (irradiation nozzle) are mounted on the gantry cylinder.
The mass of a beam transport system, which includes the aforementioned beam transport device and irradiation device, is used to generate a moment about a rotation axis of the rotating gantry. It is preferred that the moment about the rotation axis of the rotating gantry be minimized in a resting state. Therefore, the gantry cylinder includes a balance weight, which generates a moment that is oriented in a direction opposite to the direction of the moment generated by the beam transport system, and ensures that the moments about the rotation axis are balanced in the resting state.
The rotating gantry is supported at the positions of the front ring and rear ring by radial support devices having a plurality of freely-rotating rollers. The plurality of freely-rotating rollers, which are provided in each radial support device, are in contact with the front ring or rear ring. The rotating gantry rotates when some of the rollers are rotated by motors. The rotation of the rotating gantry orients the irradiation device so that an ion beam is incident on the affected part of the body.
In a rotating gantry for a particle beam therapy apparatus that is disclosed in Patent Document 2, a rear ring is supported by a support device with rollers, whereas a front ring is supported by a front support frame, which is mounted on a base section, via a swivel ring. The swivel ring is used so that the rear ring is rotatably mounted on the front support frame. The front support frame is mounted on a leg section, which is pivotally coupled by a pin to the base section. The pin is used so that the leg section can be tilted in the direction of the rotation axis of the rotating gantry. Therefore, the rear ring can also be tilted in the direction of the rotation axis of the rotating gantry. This configuration is employed to maintain the positional relationship between a bed and the rotating gantry.
A rotating gantry for a particle beam therapy apparatus is also referred to in Patent Document 3. This rotating gantry includes two rotating rings, which are supported by respective rollers. To maintain consistent rotation center position accuracy for a long period of time, a pair of drive rollers rotate at least either one of the rotating rings while the rotating ring is sandwiched between the drive rollers with both of its lateral surfaces brought into contact with the drive rollers.
Patent Document 4 also refers to a rotating gantry for a particle beam therapy apparatus. Rotating gantry members suitable particularly for irradiation with a carbon ion beam or other heavy particle beam are disclosed in this patent document. This rotating gantry includes a primary member, which is rotationally symmetric, and a secondary member, which is supported by the primary member to retain a bending magnet. A flexible, rigid member for providing a uniform amount of vertical displacement due to the bending magnet's own weight at all rotational angular positions is used as the secondary member to reduce the weight of the rotating gantry. In addition, the rotating gantry also includes a front ring and a rear ring. The weight of the rotating gantry is supported by a radial support device at a position of each ring. The employed design is such that either the front radial support device or the rear radial support device can be moved toward the rotation axis.    Patent Document 1: JP-A-11-47287    Patent Document 2: JP-A-2000-140134    Patent Document 3: Japanese Patent No. 3599995    Patent Document 4: JP-A-2004-148103